


Shattered Dreams Are More Poetic Anyways, Right?

by hyliank8



Category: Undertale (Video Game)
Genre: (which gaster Heavily takes advantage of), Abuse of Authority, Angst, Big Brother Sans (Undertale), Choking/Suffocation, Dissociation, Emotional Manipulation, Evil W. D. Gaster, Gaster is an irredeemable piece of shit, Heavy Angst, Hurt No Comfort, LOTS of tags on this one but i want people to be Properly Warned, M/M, Naivety, Pining, Praise Kink, Sex Magic, Size Difference, Soul Rape/Non-con, Soul Sex, Temporary Blindness, Unhealthy Sanster, Unrequited Crush, Vaginal Fingering, W. D. Gaster is not related to Skelebros, Younger Brother Papyrus (Undertale), be warned that sans is a Young adult, blackmailing, gratuitous pain for poor sans, it's not rly a pussy but close enough, soul manipulation
Language: English
Status: Completed
Published: 2020-07-19
Updated: 2020-07-19
Packaged: 2021-03-04 19:09:06
Rating: Mature
Warnings: Rape/Non-Con
Chapters: 1
Words: 7,186
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/25371415
Author URL: https://archiveofourown.org/users/hyliank8/pseuds/hyliank8
Summary: After years of work in the labs, Sans is promoted to be the personal assistant of the famous Royal Scientist, Dr. W. D. Gaster.  He's excited that he gets to work with somebody he's looked up to so intently for so long; all of his hard work seems to finally be paying off!...But as it turns out, the job isn't what he expected.
Relationships: Papyrus & Sans (Undertale), W. D. Gaster/Sans
Comments: 26
Kudos: 58





	Shattered Dreams Are More Poetic Anyways, Right?

**Author's Note:**

> hello everyone this has been in the works for literal months but i reached Darkfic Burnout™ three (3) times while writing LOL
> 
> this is actually based on some art my good friend made a while ago!! it's since been removed, but the memories/parts in italics have dialogue directly from the art... it was a while ago though so i think i got some of the dialogue slightly off,, hopefully i didn't misrepresent it too much
> 
> also pls be warned (as stated in the tags) that sans is a pretty young adult here, probably somewhere between 19-23, and it shows a bit
> 
> this is. the longest, and probably most fucked thing i have written. so i will now b posting this, and backing away slowly,
> 
> enjoy!!

“Sit on the bed and take off your lab coat.”

The bed in the center of the simple room is quite large, and the pure white bedding is tucked meticulously around the edges of the bed in a manner that is distinctly reminiscent of the clean, organized state of the rest of the lab. The room is cool, a few degrees below what most monsters would consider comfortable. 

Sans shivers involuntarily, though he’s not sure that the temperature of the room is entirely to blame for his discomfort.

He didn’t expect his new job as Doctor Gaster’s assistant to bring him to the scientist’s private quarters. Hell, he didn’t even expect the doctor to _have_ private quarters in the lab—does he stay overnight that often? He supposes it makes sense that the scientist would end up spending least some nights here, given how absorbed Sans has seen him become in his work before.

Not that it matters what Sans does or doesn’t expect. He’s here to do what Doctor Gaster tells him to do, here to impress him and show him that he’s capable of… whatever it is that Gaster wants, exactly. But Sans is having a hard time pushing back his nervousness, and he hesitates.

Doctor Gaster seems to sense that.

“...Unless… you believe I should seek out someone else more suited for this position?” The Royal Scientist prompts, voice laced with impatience.

“n-no, no,” Sans says, quickly taking a step forward to obey the doctor. The prompting is enough for him to push away his trepidation, even if only temporarily. “i’ll do as you say.”

—

_“pap, hey, look!” Sans proudly presents the document announcing his promotion, bubbling with excitement. “i got a promotion to be the royal scientist’s personal lab assistant!”_

_He’s been working so hard for so long, trying with everything he has to show his bosses that he was worthy of such an honor. His brother saw how exhausted he was coming home from work some days, how tirelessly he’s worked himself day and night for a shot at this promotion. And now he has it!_

_He’s… had a little bit of a crush on the Royal Scientist as well, if he’s honest with himself. The elegant way Doctor Gaster holds himself, the eloquent way he speaks, the endless knowledge he seems to possess… Sans can’t help but have such a deep admiration for him. All of his work has been revolutionary, changing the lives of everyone who lives in the Underground. Even alongside the joy of being able to get a head start on his career, the thought of getting to work so closely with the scientist makes Sans’ face flush warm with his magic._

_Sans tries to push his crush to the back of his mind. It’s not like he’s ever been in a relationship before, and he’s sure someone like Doctor Gaster wouldn’t be interested in his inexperience._

_“Really, brother?! That’s awesome!!” His little brother exclaims with all the genuine enthusiasm he has to offer. “We should celebrate!!”_

_Sans chuckles happily. Papyrus is such a sweet, supportive little brother. There’s such genuine happiness on his face, like he’s really sharing in Sans’ joy. The thought that this promotion may help him provide for his little brother better, that the extra income may help him buy his little brother new clothes, new school supplies, maybe even some puzzle games—it fills him to the brim with a hope he hasn’t felt in so, so long._

_He can’t wait for his first day._

—

“You have such lovely bones, Sans,” the Royal Scientist observes as Sans continues to undress. There’s an eagerness in his voice that sends shivers down Sans’ spine.

He’s not sure he likes the way that feels, but he continues what he started regardless, slipping his shirt off next as Doctor Gaster instructed.

—

_“So, he’s the new assistant for Gaster?”_

_Sans can’t help but hear the murmurs around the labs as he goes about his work. He supposes he should have expected some gossip, what with occupying such a heavily sought-after position in the Royal Scientist’s labs._

_“I feel sorry for that guy.”_

_Sans’ walk falters for a moment. Did he hear that right? He shakes his head lightly and continues with his brisk pace, carrying his reports to one of his new colleagues. He hopes his position isn’t causing anyone jealousy—that’s the very last thing he wants to have to deal with, but he supposes it could be expected with how lucky he is to have this position._

_But where he expected the tinge of sarcasm to bite at the passing monster’s words, there seemed to be untempered sincerity… did he read their tone incorrectly? He’s the assistant for the smartest monster in the Underground now! How could anybody feel sorry for him?_

_Maybe they’re worried about the quantity and difficulty of the work—it certainly hasn’t been easy so far. But that’s okay; he’ll show them all that he can handle it!_

—

“Lay back,” Doctor Gaster commands.

Sans does as he’s told immediately, lying back against the rather firm pillows. He feels utterly exposed with his ribcage naked to the chilly air, and his soul beats unsteadily in his ribcage as nervousness pulses through his bones.

He flinches when the doctor’s cool hands brush his iliac crests, pulling at the waistband of his shorts. He’s not sure if Gaster has noticed his startle, but Sans swears he sees the hint of a smirk twitch at the corner of the doctor’s mouth for a moment. But Sans blinks and it’s gone, no hint left in the elder monster’s cool composure that there was any reaction in the first place. 

Surely, Sans’ nerves are playing tricks on him.

Sans lifts his hips, and Gaster pulls off his shorts in one smooth movement. Sans shivers as the air invades the intimate spaces between the bones of his pelvis. Gaster wastes no time leaning down to Sans’ level to meet his gaze, a smile quirking the corner of his mouth. The dark and leering look shining in Gaster’s eyelights sets Sans on edge, yet he can’t control the excitement that throbs in his soul simply from how _close_ he is to the monster he’s admired for so many years.

“Now, give us a kiss, won’t you, Sans?”

Sans’ soul starts. _kiss him?_ He’s taken aback by the request, though he supposes he’s not entirely sure why. It’s certainly no more demanding than anything Gaster has asked for already, but… kissing seems so _intimate_.

“Oh, there’s no need to be so coy, my dear assistant,” Gaster supplies, easily reading Sans’ expression for what it holds. “I know how long you’ve wanted this.”

Sans’ face flushes in lieu of a real response, mentally scrambling for something to say in reply. What can he possibly say to that? What does Gaster even _mean_ by that? Gaster chuckles darkly at his reaction and continues before Sans can come up with anything.

“Yes, your soul is very unique, isn’t it? I felt it call out to me as I made rounds in your sector of the lab, you know.”

Sans opens his mouth in preparation to respond but still is at a loss for a meaningful way to defend himself. Stars—Gaster made his way around to check on the lower labs’ experiments fairly often, and Sans remembers the heat that rushed to his face whenever he saw the tall monster, remembers how distracted he would become with the doctor’s presence…

Did Gaster know how he felt that entire time?

“i… i’m not sure i—”

Gaster leans closer, their faces now nearly touching. The sensation of the doctor’s warm breath on his mandible is exhilarating; despite his trepidation, an unmistakable heat buds in his soul.

“Let’s give it what it wants, shall we?” Gaster breathes.

He leans in and locks Sans’ mouth in a deep kiss, Sans’ soul sparking with heat as he automatically reciprocates.

The doctor wastes no time, quickly moving to coax Sans’ teeth apart to work Sans’ conjured tongue with his own. Sans can’t help but groan into the kiss, overwhelmed with the new sensation, with the taste of the doctor’s tongue. The taste is so uniquely _him_ —it’s clean like the labs he runs, laced with a faint bitterness akin to that of the black coffee the scientist drinks so often. He can’t help but be absolutely enthralled with the taste, and Gaster’s tongue against his own feels so unbelievably _good_. Sans hopes he’s doing this correctly, hopes the doctor is pleased with him… he’s never kissed anyone like this before.

Gaster shifts his position, moving his body more directly over Sans’ and letting his hands wander over his small assistant’s bones, playing with his ribs, caressing his sternum, moving down his sensitive spine to his pelvis.

Sans shivers at the demanding touch.

—

_“Ah, Sans,” Doctor Gaster says coolly. “I was expecting you.”_   
  
_“doctor gaster, sir!” Sans says, trying hard not to blush at how close he is to the Royal Scientist. Doctor Gaster smells so nice… clean and clinical, just like his labs, but there’s something personal about the scent, too._

_Sans makes a conscious effort to focus on his excitement instead of the attractiveness of the tall monster in front of him. “thank you for choosing me! i’ll try my best, sir!”_

_His fists clench nervously at his sides. He’s sure he’s coming across as enthusiastic, and that’s a good thing, right? Oh no, does he sound too eager? He sure hopes not. He just wants to do his job well, that’s all! Nothing more to it than that!_

_Maybe he could even be promoted further in the future. With that pay, he could support Papyrus so well… Sans imagines buying his little brother all the things he deserves, maybe even getting him that fancy oatmeal that he likes so much. He imagines the big smile he’d get from the little skeleton, how it would stretch across his cheekbones; being able to see such a happy expression on his little brother’s face would be worth all of the hardest work the world has to offer. Papyrus is a good kid, has always been a good kid and Sans has had no shortage of guilt for not being able to provide for him as well as he feels like he should have._

_And now he has a chance to change that._

_“...Of course, please try your best in pleasuring me, Sans. I really do like you, and it would be a disappointment if you were to fail to fulfill your purpose.”_

_...Pleasuring? That wording conjures a few pictures in Sans’ mind that makes his face flush. He blinks hard, trying to rid himself of both the mental images and the magic that has heated his face. Sans scolds himself for letting his infatuation with the older monster take that much control of his mind for a moment—of course Gaster’s just talking about pleasing him with his work ethic; nothing more than that._

_“ah… sure thing, doctor,” Sans stammers uncertainly, unable to get his mind off of the peculiar phrasing. “thank you, sir.”_

—

It doesn’t take long for Gaster to figure out how to guide Sans’ magic to coalesce into something he can use.

Gaster’s fingers roughly massage Sans’ sensitive pubic symphysis, coaxing light pants and soft moans out of the smaller monster. Sans bit down on his noises initially, but Gaster insisted that he let his voice be heard. Sans reluctantly obliged, and he lets a pleased sound slip through his teeth every so often, but still works to keep control over his voice. 

Sans feels an unfamiliar heat building in his soul, and he’s somewhat uncomfortable with the intimacy of all of this, but—at the same time it feels really, really good, so he supposes it’s not all bad. He can’t deny his continued excitement at being so close to the Royal Scientist, too, even if it’s beginning to feel a little bit… too close. Part of him wishes Doctor Gaster had let him keep at least _some_ of his clothing on—he feels especially bare with the doctor fully clothed in comparison—but the more vocal part of his mind is too eager to please to perseverate on his own discomfort.

Gaster chuckles at yet another whimper that Sans fails to contain, his tongue lashing out as he leaves a wet, greedy kiss on Sans’ vertebrae. It’s not long before magic fills the base of Sans’ pelvic inlet, forming a thick, pliable wall of his magic that Gaster doesn’t hesitate to push into with two long fingers.

Sans gasps at the odd sensation, at the way the layer of magic stretches for Gaster’s fingers as it engulfs them. He grasps at the back of Gaster’s lab coat, desperate for something to anchor him in the midst of the weird, new sensation. It’s not exactly… unpleasant, he has to admit, but he’s not used to using his magic like this; he’s not a stranger to touching himself, but it’s rare that he gets his magic involved. As Gaster begins to thrust into his magic, the heat in his soul rises, and Sans finds he has to clench his teeth to keep himself from making any particularly shameful sounds.

Gaster continues working him with his deft fingers, and Sans finds it increasingly difficult to stay quiet. His fingers twist into the back of Gaster’s lab coat and into the sheets as his fists clench involuntarily, his soul growing hotter as Gaster continues his thrusting. Gaster curls his fingers inside of him on the next inward thrust, finally jarring a small, pleased cry out of Sans.

A conniving smirk lifts the corners of Gaster’s mouth. “Mm, you like that, don’t you?”

Sans’s face flushes hot with embarrassment, but he doesn’t want to risk leaving Gaster’s prompting unanswered, rhetorical as it may have seemed. Reluctantly, he nods.

A few moments later, Gaster pulls his hand free of Sans’ magic. He slips his slicked fingers into his mouth, sucking them clean of Sans’ essence, and something about seeing that sparks something hot and primal deep in Sans’ soul.

“Mmh, you taste wonderful, Sans,” Gaster murmurs. “I think you should taste this, too.”

Before Sans has a chance to understand what that means, Gaster leans forward and captures Sans’ mouth in another heated kiss. There’s a taste on Gaster’s tongue this time that’s different from his usual clean, coffee-tinged taste… it’s odd and makes Sans feel self-conscious, and he’s not sure he likes that. But he can’t deny that he’s been enjoying Gaster’s kisses, so he tries to focus on that instead of the taste.

The kiss continues for longer than Sans expects. With Gaster’s tongue working against his so roughly and the scientist’s face so close to his, it’s beginning to feel more difficult to get the air he needs and it’s not long before Sans finds himself breathing heavily.

Gaster’s weight adjusts above him as Sans hears the pull of a zipper down below. He doesn’t feel the doctor’s arms move, though… did he summon one of his auxiliary hands at his waist to do it for him? Sans can’t move his head to look down, locked as it is in the doctor’s kiss. 

His idle curiosity is overshadowed by the sudden realization of what exactly Gaster must be intending next. Stars, are they really doing this? He’s not sure he’s ready for something like— 

Sans’ thought is cut off when Gaster pushes harshly into his magic below, a pained gasp catching in his throat.

Fear sparks wildly in Sans’ soul as hot pain flares up in his pelvis. His mouth is still occupied and he whimpers, tries to get Gaster to notice his pain, curls his toes and tries to kick his legs but the larger monster’s immense weight has his entire body pinned firmly against the bed. He feels like he’s choking on Gaster’s tongue as Gaster continues pushing his hips forward, groaning into the demanding kiss until he’s sheathed himself inside of Sans completely.

Panic grips Sans’ soul. God, he’s never been with anyone like this before, and the intimacy, the distinct awareness that he has nowhere to hide is suddenly absolutely _terrifying_. It’s new and scary and painful all at once and it’s _too much_ , the pain and the fear are suffocating him and he _needs_ Gaster to stop this right now.

Finally, Gaster pulls back from the kiss, and Sans heaves for air as though his head has been held underwater.

“doctor gaster,” he gasps desperately, trying to shift his body to sit himself up. It’s no use; the doctor has him trapped. “that hurts—”

“Shh… quiet now, my boy,” Gaster croons, cutting off Sans’ protest smoothly. He rests his hand on the smaller monster’s rib cage, keeping him down with minimal effort. Sans is suddenly acutely aware of how huge Gaster’s hand really is compared to him—its span nearly covers the entire front of his rib cage. “You’re doing very well; remain still.”

The praise keeps him quiet for a moment as Sans struggles to catch his breath, trying to rein his breathing back into a normal tempo. He can do this, he tells himself, he can do it; Gaster said he’s doing well, he’s doing a good job, he’s fulfilling his purpose, maybe he just has to get used to the pain until Gaster’s satisfied, and until then he can just—

His calming thoughts evaporate the moment Gaster pulls out and thrusts into him again, rougher than the first time. Without Gaster’s mouth on his, there’s nothing preventing Sans from crying out immediately and openly this time, tears springing to his eyes. 

“wait! _stop!_ ” he cries desperately. He pushes his palms against Gaster’s chest, praying that the larger monster will understand his pain and desperation and pull back—even a _little_ bit would be better than this. But he doesn’t, and Sans feels his magic tearing under the assault and _it feels like he’s being ripped apart and he can’t take it_. “doctor gaster, _please—!_ ” 

Sans is forced into silence when a magic hand clamps firmly over his mouth. Two more materialize in the same moment and rip his hands away from where they were pushing against Gaster, pinning them against the bed on either side of his head by the wrists. The harsh motion leaves Sans breathless. “I said be _quiet_ , Sans,” Gaster says lowly. “This is your _job_ , remember? It would be _very_ aggravating to me if I had to find another assistant to take your place, you know…” The threat is thick in his voice, and the dangerous tone freezes Sans’ soul with fear. 

Doctor Gaster’s size and strength have never been more apparent to Sans than they are now, and with the way the doctor has him pinned Sans doesn’t want to think about how helpless he would be if Gaster decided to act out of his aforementioned _aggravation_. 

Any previous excitement he felt from being so close to the monster he admires so much has long morphed into fear.

Gaster releases his mouth to allow him to speak, but Sans takes Gaster’s words to heart; he doesn’t respond, instead carefully nodding in silent acceptance of the larger monster’s words as he blinks back his tears. Despite his efforts he’s sure his fear must still be creeping into his expression, but Gaster… doesn’t seem to mind that, if his lack of comment is any indication.

“Good boy. I suppose I can be more gentle with you since you’re being so good.”

 _please_ _, thank god_ , Sans thinks, daring to allow his relief to melt away some of his fear.

Gaster pulls out of him slowly this time, capturing Sans’ mouth in another deep kiss before pushing back inside of him just as gradually. It’s still painful, but it’s manageable. Sans’ magic is a bit raw from Gaster’s initial roughness, but he can bear it now at least while managing to keep the tears at bay. He stomps his fear back down and focuses instead on the kiss to try to distract his mind—after all, he’s fantasized about being able to kiss Doctor Gaster for a long time, about being able to be close to him, so he should be grateful for this… right?

Gaster establishes a gentle pace rocking into him, moving his kiss from Sans’ mouth down to his jaw, eventually reaching his cervical vertebrae. He nips at the delicate bone lightly, eliciting a small moan from Sans. Sans flushes and snaps his mouth shut, embarrassed by the sound that left him, but Gaster only chuckles lightly and repeats the action languidly, clearly aiming to get the reaction out of his small assistant a second time. 

Gaster’s self-control wanes rather quickly. It doesn’t take long for his movements to regain their strength, his gentle rocking rapidly devolving into rougher thrusts. With the added force, it becomes harder and harder for Sans to let the pain fall at the back of his mind. Even alongside his efforts not to humiliate himself with his shameful sounds, Sans continues making an enormous effort to focus instead on Gaster’s gentler attentions, on his warm, wet tongue, on the pleasant, warm feeling it leaves on his vertebrae.

“Your magic is so beautiful, Sans, so _good..._ ” Gaster groans, punctuating his statement with another harsh thrust that has pained tears welling up in Sans’ eye sockets all over again.

Sans grasps onto the praise like a lifeline, repeating the doctor’s words over and over in his mind— _beautiful, he said, so good, good i’ll be_ _good _ _i can do this i can i swear_ —as if that will stop the hurt from reaching him, as if forcing Gaster’s satisfied tone to occupy the forefront of his mind will push away the hot pain.

Gaster groans wordlessly and halts his movement, and for a desperately hopeful moment Sans thinks the scientist is finally finished with him.

He’s wrong. Gaster only shifts his weight to allow himself to look Sans in the eyes. It’s strange to Sans to see the scientist looking so disheveled—he’s panting, sweat beading on his brow, his eyes hazy with pleasure. It’s so unlike the calm, composed expression he’s grown accustomed to admiring on the scientist’s face as he works.

He’s unprepared for Gaster’s next command.

“Call forward your soul.”

Sans freezes. 

He’s certainly _heard_ about soul-sharing before, but he never thought he’d ever consider doing such a thing. It’s one of the most intimate acts between monsters, seen as an indication of trust on a level above all others. The soul is the culmination of a monster’s being—for a monster to share their soul is for them to put everything about themself on display, entrusting the raw essence of their life and their existence to another. It’s a deep and powerful experience to feel the untempered flow of emotion and magic between two souls, an experience without barriers that is intended only between the closest of monsters.

For Sans, the thought of opening himself up like that to anybody is terrifying. Surely, with the lack of barriers would come an unparalleled risk for hurt, for manipulation, for pain… wouldn’t it?

“my… soul?” 

“Yes, Sans. Hurry up.” The haziness of Gaster’s eyelights doesn’t hide the impatience that twinges in his expression.

“o-okay, okay.” Sans is desperate not to mess this up, Gaster’s threatening tone from earlier still ringing in his skull. He pushes his worries aside and quickly focuses his magic inwards, focusing on his soul’s delicate presence. With great care, he pulls the small, inverted heart forth to appear in front of his sternum.

A deeply instinctive section of his mind immediately protests with a panicked flare of _wrongwrongstopSTOPSTOPDANGER_ ** _DANGER_** the moment his soul leaves the safety of his ribcage, but Sans does his best to push that feeling away, too.

His soul glows softly, a gentle, white light radiating off of it. Sans thinks he can see it trembling, but he’s not sure whether he’s imagining it. Observing Sans’ soul, a smile plays at the corners of Gaster’s mouth, though it doesn’t reach his eyes.

“You’re beautiful, Sans.” His tone is matter-of-fact; it barely feels like a compliment, but Sans can’t help but blush regardless. Having the most vulnerable part of himself out on display is messing with his nerves in a way that is making it much more difficult to control his reactions.

Gaster’s eyes shut for a moment, and he tilts his head down, a concentrated expression on his face that Sans imagines mirrors the look he wore a moment ago when he called upon his own soul.

The moment the flash of Gaster’s soul appears in front of his chest, Sans is overwhelmed with an intense wave of unfiltered emotion that he can distinctly tell _doesn’t belong to him_. It’s _lust_ , Sans realizes with a pit of dread in his soul, and it radiates off of the doctor’s soul in dominant surges. If Sans wasn’t sure whether his soul was trembling before, he’s _certain_ it is now. 

Sans winces and squeezes his eyes shut for a moment, forcing himself to adjust to the unyielding presence of the culmination of Gaster’s being. It’s almost unnatural, the waves of sheer _power_ he feels from his superior’s soul—he didn’t realize it was possible for a monster to have such strong magic. The feeling fills the space between the two of them and leaves Sans struggling to feel even his own soul in its midst, as though the connection between himself and his magic is being tampered with. It’s hard to breathe with the doctor’s soul so close to his own; primal fear crawls through him as he is forced into awareness of the fact that he’s in the presence of a soul far more powerful than his. That with his soul bared like this, he is helpless and entirely at the mercy of a monster far stronger than him.

When Sans is finally able to open his eyes, the first thing that hits him is the sheer _size_ of Doctor Gaster’s soul compared to his. His own soul is dwarfed by it, the white light drifting off of it nearly blinding when compared to the duller glow of his own. A few cracks mar the surface of it, infused with a deep purple hue that somehow shines while simultaneously devouring the light that surrounds it. Distantly, Sans wonders what could have happened to Gaster’s soul—he’s never heard of a soul that has cracks that look like that before.

Another realization occurs to Sans as well—for some reason, he’s not experiencing the scientist’s thoughts as he thought he’d be able to once their souls were within close and intended proximity to one another. Sans can’t detect any nuance to his emotions, either—all he feels from Gaster is that same deep, overwhelming desire that makes his own soul flutter with unease. Gaster’s mind remains hidden from him.

“Aw… no need to be so frightened, you sweet thing,” Gaster croons.

And apparently Gaster can see into _his_ mind just fine.

“I’ll take good care of you.” Doctor Gaster reaches a hand towards Sans’ soul before Sans has a chance to predict his intentions.

“w-wait, i don’t know if this is a good—”

Sans is cut off with a gasp when Gaster’s hand closes around his soul. 

The direct contact with the most vulnerable part of him sends a jarring, icy sensation pulsing throughout his entire body all at once. Gaster pulls Sans’ soul closer to his chest, forcing their souls even closer together. Sans is assaulted directly by the raw magic Gaster’s soul produces, and it’s unlike anything he’s ever felt before; it’s as though all of his senses are being filled with Gaster’s presence, his magic, his primal desire, leaving no room for Sans’ own thoughts or feelings.

Sans hasn’t yet caught his breath when Gaster pushes his own soul forward, forcing the surfaces of their souls to touch.

Sans cries out at the scorching waves of heat that crash into him all at once. It’s as though he’s being assaulted from all sides; the alarmingly incorporeal feeling pulses through his soul, sweeping his mind clean of any coherent thought he had left. 

He can’t stop himself from trying to scramble away, _he has to get away_ but Gaster still has his hands pinned to the bed and he’s completely unable to move. He can barely _breathe_ the feeling is so intense, and he realizes a moment later that that’s a problem, that his soul is so overwhelmed that he can’t take in the air around him properly anymore. And when he opens his mouth to protest only for his words to get stuck in his throat, he’s struck with the realization that for that same reason he can’t _speak_ anymore, either. Mindlessly panicking, he struggles against Gaster’s grip, trying to pull his wrists free, but Gaster’s weight holds him down effortlessly. Even without the ability to properly speak, a tormented whine tears from Sans’ throat as Gaster thrusts into him once more. 

“F- _fuck_ ,” Gaster gasps. “That’s a good boy… stars, your magic is so _weak_ , Sans, it’s like you were _made_ for this…”

Sans hardly registers the pleasure, the sick appreciation in the doctor’s tone, hardly registers the fact that Doctor Gaster seems to _enjoy_ that Sans is weak and defenseless and utterly at his mercy—it makes Sans’ magic churn horribly in his soul but he can barely spare a thought to it in his breathless panic. Gaster’s soul is so powerful that Sans feels like it’s overtaking his own, like Sans doesn’t exist anymore and he’s just an extension of Gaster, a toy for him to play with, to use, as though he’s been completely robbed of an existence outside of Gaster’s presence. It’s painful and it’s _too much_ but Sans can’t find his words to protest. His tears spill over and he’s far too overwhelmed to care that he can’t stop them anymore.

Gaster presses his soul into Sans’ further, and Sans chokes. The presence of the doctor’s magic is suffocating—it’s not just around him, it’s around his _soul_ , it’s invading the culmination of his being and he _needs air_ — 

“doctor gaster,” Sans manages to croak out. His voice is so _tiny_ , but it’s all he can manage.

 _you’re smothering me,_ _please_ _—_

The scientist groans, giving another rough thrust of his hips that knocks Sans’ breath even further away. He rocks into him again, harsher than before—Gaster’s in him so deep and Sans’ magic is stretching for him and it _hurts_.

“So fucking _good_ ,” Gaster sighs as though he’s heard nothing. “You feel _amazing_ , you sweet thing.”

Sans thinks Gaster might have said something else, too, but it’s getting harder to focus on anything that he’s saying, harder to focus on anything but the pressure around his soul. It’s _him_ , it’s his entire existence, everything that makes him who he is is being stifled, suffocated, forced to submit to a monster so much more powerful than him.

God, Sans can’t—he can’t do this. He has to, but he can’t, he needs this position, he has to do this for his brother, has to do it for Papyrus but he can barely feel his own _soul_ and it’s _too much_ — 

“doctor gaster,“ Sans gasps, finally forcing his voice through the suffocating layer of Gaster’s magic. “it’s hard to breathe, please—my soul—“

Gaster still doesn’t respond. Sans wheezes frantically, his vision beginning to blur around the edges. He’s terrified—he’s never worried about breathing before, but now it feels like he’s drowning, like someone’s thrown him into the furthest part of Snowdin’s river and left him to swim upstream all on his own as the freezing water leeches the energy from his limbs. He tries desperately to catch Gaster’s eyelights, to do _anything_ to communicate with him since his voice is clearly too weak to catch his attention, but Gaster’s not even looking at him anymore—the scientist’s eyes are shut in bliss and his teeth have caught the edge of his lip, his brow furrowed as he focuses solely on the sensations.

Sans blinks hard, trying to dispel the splotches of blackness that have invaded his eyesight, but it doesn’t work. The dark spots only grow, larger and larger until they’ve consumed his vision and his surroundings have faded entirely. At first he thinks he’s lost consciousness, but when the pain doesn’t fade it becomes clear that it’s only his eyesight that has failed him. And he has a scary idea about why that could be happening—he knows that when his soul is deprived of basic nourishment, the magic that regulates his senses is put under too much stress to function properly. 

The last time he experienced any loss to his senses was years ago, back when he and Papyrus were living on the streets, during a particularly rough week when Sans hadn’t found enough food to sustain the both of them. But Sans has never been robbed of his senses so _suddenly_ before, never had his soul submerged in the powerful, unforgiving magic of another monster. 

He can’t do this.

“doctor, please,” he croaks. He’s _desperate_ but no matter how hard he tries, he can’t force any more volume into his voice than before. “i can’t s-see—you’re strangling my s-soul, it’s—it’s—” _killing me, you’re killing me,_ he wants to say, because he’s certain that if Gaster doesn’t let up soon he’s going to die; there’s no way that this amount of suffering could end in anything other than that. Yet even with the terror that consumes him he maintains the distinct fear of the wrath Gaster unleashed the last time Sans begged him to stop. “you’re gonna r-really, really hurt me, please, please don’t—” 

“You can take it,” Gaster grunts breathlessly. It’s the only indication that he’s heard any of Sans’ pleading up until this point, and the implicit confirmation that Gaster has clearly heard him from the start makes Sans’ soul twist horribly. He can’t even see Gaster’s face anymore—but from the tone, he’s sure the scientist’s expression hasn’t changed, that he’s still focusing solely on his pleasure, callous to the turmoil of the helpless monster beneath him.

“n-n—” _no, you don’t understand_ , he wants to say, and Sans can’t force out another word but he can’t take it, he _can’t_ , he’s sure that if Gaster doesn’t let up he’s going to die. 

Gaster’s thrusts only increase in speed as he forces his soul further against Sans’, and with horror searing in his magic Sans wonders if it’s possible for Gaster to drive them to bond. Sans thought that a soul bond would require his own intent to help it along, but he doesn’t know much about souls or soul sharing, and after another agonizing thrust Sans decides that it doesn’t even _matter_ , all he knows is that he _needs Gaster to stop_.

He desperately tries to move his legs again, to kick, to do _anything_ because he’s more scared than he’s ever been and he doesn’t want to die, he can’t die—what would Papyrus do without him? He can’t die, he doesn’t want this anymore, he doesn’t care if he has to go back to living on the streets, he’ll go back to scavenging and starving he just doesn’t want— 

Gaster lets out a loud groan above him, and Sans can’t even cry out when his soul is abruptly flooded with an unwanted wave of unbearable heat. Sans can tell the feeling is still not his own—it flows from Gaster’s soul in powerful pulses, forcing all thoughts of protest from Sans’ mind in its wake.

In jarring contrast to the pain that filled his soul before, Sans realizes some deep part of his mind categorizes the feeling as _pleasure_ —but it doesn’t feel good. It’s overwhelming and somehow even _worse_ than what he was already feeling. There's a distinct sharpness to the heat that cuts into his very soul, as though it’s forcing its way into the foundation of who he is.

Even robbed of his sight, Sans can feel the room spinning around him as Gaster’s thrusts gradually slow. Sans weakly tries to free his hands from Gaster’s hold once more, but the scientist’s iron grip hasn’t faltered in parallel—and Sans doesn’t have the strength to fight him anymore.

Just as Sans feels his consciousness fading, the pressure around his soul begins to ebb. Gaster eventually halts his movement, the weight keeping Sans pressed against the mattress gradually lifting as the larger monster pulls back. 

Sans has little warning before their souls finally separate, leaving him gasping desperately for the breath that eluded him before. The absence of Gaster’s soul is sudden and jarring, and it leaves Sans feeling dizzyingly off-center and disconcertingly bereft. Sans makes a conscious effort to ignore the ache that has bloomed where Gaster’s soul broke away from his own.

As his soul regains the nourishment of the air that it has so long been denied, Sans’ sight gradually returns. It fades back in slowly, the darkness melting away and allowing Sans’ eyelights to fall onto Gaster’s calm, pleased expression.

Distantly, Sans realizes he feels something wet dripping onto his sternum. Still dazed, he glances down to find his soul dripping with a sickening mix of blue and purple magic, the two fluids dancing around one another and meshing until they’re the hue of neither his boss’ magic nor his own. 

There’s… something off about his soul beneath the colorful mix of magic, too. A dark overlay covers the surface of his soul with a purple tint, the naturally hearty glow of his soul faltering to a dim, paltry light.

“My, my, look at that,” Gaster grins. There’s a note of wicked pride in the doctor’s tone, his eyes hungrily locked on the small, inverted heart beneath him as he observes the way his magic taints his subordinate’s soul. “I’ve made quite the mess of you, haven’t I?”

Sans feels sick.

Ignoring the visceral desire to wipe his soul clean of the disgusting mix of soul fluids, Sans delicately pulls the culmination of his being back into his ribcage. 

He tries to open his mouth to speak, to give some sort of response—he’s not even sure what he wants to say, but he feels like it’s a bad idea to leave any one of Gaster’s statements unanswered—but his energy has completely left him. He resigns himself to lying limply against the now-ruined sheets as he continues his struggle to catch his breath.

The doctor draws back further, finally pulling out of Sans’ magic below with a satisfied sigh. Another sticky fluid seeps out in his absence. 

Sans has never so badly felt the need to throw up. It's disgusting. He’s disgusting.

Sans promptly dispels his magic, leaving the doctor’s release sticking sickeningly to the base of his pelvis. His soul continues to drip as well, coating his spine in their mixed magic, but he’s far too fearful of his boss’ potential retaliation to make any move towards cleaning himself.

“You’re resilient,” Gaster observes, still breathless. “Few others before you have done as well as you have.” 

_Before you_ , Sans realizes with awful clarity. That’s what the gossiping monsters meant. The genuine sympathy in their hushed voices—they knew. They knew what Sans had been chosen for, what responsibilities he was undertaking by accepting this position.

Sans’ soul clenches painfully at the doctor’s half-hearted praise. This is what Gaster wanted him for, wasn’t it? Not his accomplishments, not his hard work. Just some helpless weakling to fuck when the desire arises. A stupid, naive monster far too pathetic to defend himself.

Sans doesn’t bother trying to hide his tears anymore. He lets them flow silently down his cheekbones.

It doesn’t matter. Nothing he’s been working towards matters.

Gaster hums contentedly, leaning down and leaving a gentle kiss on Sans’ cheekbone as he buttons up his pants. Sans would flinch away if he could, still distinctly uncomfortable with Gaster’s insistence upon such deceivingly gentle intimacy, but the energy required for his reflexes clearly has not yet returned.

“Mm, I suppose I may have been a bit eager,” Gaster relents upon Sans’ continued silence. “Perhaps I’ll be more gentle with you next time.”

A pit of dread blooms in Sans’ soul at the promise of a _next time_ implicit in the Royal Scientist’s wording.

Sans focuses on his breathing, trying to keep it steady. Focuses on the calming of his traumatized soul in an attempt to give himself time to catch his breath.

He tries to forget the clear purple tint his soul developed beneath the mix of their fluids. How off-balance he felt when Gaster’s soul finally separated from his. 

He doesn’t want to think about whether or not his soul could survive a _next time_.

—

The door to Doctor Gaster’s personal quarters slides open. Sans stands at the entrance, half-dressed and carrying the rest of his clothing tucked under a shaky arm. 

He stares emptily out into the hallway for a moment, frozen.

Shellshocked.

“...huh,” he murmurs aloud. _so that’s really what the royal scientist’s assistant does._ The job he was promoted to, the job he was chosen specifically for. This is his purpose, now.

His soul still drips in a way that makes him feel nauseous, the inside of his rib cage now soaked with the excess magic. His eyes burn with tears that he can no longer shed. 

He forces himself to take a step forward, ignoring the disgusting wetness that drips down his femur and onto the tiled floor of the lab. His pelvis burns, and he can’t help but limp as he walks away, not entirely sure where he’s going. He has to get dressed, right? And go home. Something like that.

Yeah, that’s right. Papyrus is waiting for him. He’ll want to hear about Sans’ first day.

Hot shame pricks at the edges of Sans’ eye sockets.

Sans wonders if Papyrus will be able to tell what happened. If he’ll see the filth Sans feels clinging to his bones. Wonders if he’ll be able to tell that there’s something wrong with his older brother’s soul, that it’s been tainted.

He’d give anything for Papyrus not to know.

He tries to still his shaking hands as he sets out to find one of the lab’s private changing rooms. The burning in his pelvis feels more distant with every step he takes, yet he’s sure his injury hasn’t begun healing itself yet. The pain is surely still there; it seems that his ability to feel it is what is deteriorating. 

That’s okay, probably. It’s fine. _It doesn’t matter_ , he reminds himself.

“Good work today, Sans,” the Royal Scientist calls after him. “I’ll see you on Monday.”

Hours earlier, perhaps hearing such praise would have warmed his soul. 

But now, Sans doesn’t feel anything in his soul at all.

**Author's Note:**

> thank u 4 reading!! i feel like i'm not happy w/ this one Again but when i hit burnout for the 3rd time i knew i needed to finally just post LOL
> 
> im gonna shamelessly self-promote real quick and say that if u like unhealthy sanster then u might [like some](https://archiveofourown.org/works/22843840) [of my](https://archiveofourown.org/works/24329989) [other fics](https://archiveofourown.org/works/24991846) [as well](https://archiveofourown.org/works/23842138),
> 
> find me on [ twitter](https://twitter.com/K8Maybe) or [tumblr/elsewhere thru my carrd!](https://hyliank8.carrd.co/)
> 
> i hope u enjoyed! sans certainly didn't
> 
> pls consider commenting, i appreciate each n every one w/ my whole heart,,


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